1. Field of the Invention
The present invention relates to a method of treating a plating sludge. More particularly, the present invention relates to a method of treating a plating sludge, wherein a hydrated plating sludge produced during the treatment of waste liquor formed in the plating of various metals is dehydrated and dried, if necessary, together with a hydrated pickling sludge, to produce a plating sludge; the sludge is mixed with scale and dust formed in the production step of alloy steel; the mixture is molded into a briquet; and the briquet is used as a material for ferroalloy or is further subjected to a reduction smelting together with a carbonaceous reducing agent in a reduction-smelting furnace to recover valuable metals.
The term "plating sludge" herein used includes a sludge obtained by subjecting a hydrated sludge which has been formed during the treatment of waste liquor or metal plating to dehydration and drying treatments with or without sludge formed during pickling.
2. Description of the Prior Art
When waste liquor of metal plating is neutralized and then subjected to dehydration and drying treatments, a plating sludge can be separated. However, there have not hitherto been known effective methods of treating the resulting plating sludge, and almost of the sludge is used in the land-fill as an industrial waste. Such industrial waste causes public nuisance and various methods are proposed in order to solve this problem. However, all of the hitherto proposed methods have drawbacks in the treatment of the plating sludge in a commercial scale, and therefore almost of the sludge is stacked and left as it is or is solidifed by concrete and used for land-fill.
While, the plating sludge contains a large amount of valuable metals, such as Ni, Cr, Fe and the like, and it is not preferable from the viewpoint of resource saving in our country having poor resources to discard these metals after these metals are converted into harmless state. Therefore, it is very important to establish an effective method of treating plating sludge, which can recover the valuable metals.
The inventors have made various investigations in order to solve the above described problems, and proposed in Japanese Patent Application No. 5,045/76 (laid open July 25, 1977 as Japanese Patent Laid Open Application No. 88,578/77) a method of treating plating sludge, which can recover useful metals from the sludge. In the method of treating plating sludge disclosed in Japanese Patent Application No. 5,045/76, a hydrated sludge obtained from a waste liquor of metal plating is dehydrated and dried to decrease the water content to 2-20% by weight; the dried sludge was added with 2-15% by weight of an organic binder or not larger than 5% by weight of an inorganic binder or both of them, the amounts of the organic and inorganic binders being based on the solid content of the sludge, and further with water to adjust the water content of the resulting mixture to 8-30% by weight; the mixture is fully kneaded; the homogeneously kneaded mixture is molded into a briquet by means of a briquet-molding machine; the molded briquet is dried by a dryer or cured; and the dried or cured briquet is used as a raw material for ferroalloy, or is further charged into a reduction-smelting furnace together with a carbonaceous reducing agent and subjected to a reduction smelting in the furnace to recover a metal, and the metal is used as a raw material for high alloy steel.
Valuable metals contained in plating sludge can be recovered by the above described treating method, but this method has still the following drawbacks.
1. Since the plating sludge has a high phosphorus content, the recovered metal has a high phosphorus content. PA1 2. Since the dried plating sludge itself is poor in the moldability, the yield in the molding by a briquet-molding machine is low, and further the briquet is poor in the strength and causes troubles in the subsequent treatments.
The inventors have succeeded in overcoming the above described drawbacks.